Cystic fibrosis (C.F.) is the most common lethal genetic disease in Caucasians. The cloning of the gene and the characterization of numerous mutants make possible carrier screening for individuals without a family history of C.F. Therefore a pilot study is needed to determine the best method of incorporating population-based C.F. carrier screening into the health care system. The proposed project will offer C.F. carrier screening to persons of reproductive age in Rochester, New York, and quantitatively assess the resulting benefits and burdens to patient, provider, and society. Fifteen mutations will be detected simultaneously to provide 90% sensitivity in Caucasians; one goal is the demonstration that the method to be used, reverse dot strip hybridization, can provide accurate testing of many samples for many mutations simultaneously at reduced cost. Women of reproductive age are the focus of this study because their providers are the physicians most likely to offer C.F. carrier screening to their patients, because blood is drawn during pregnancy routinely, and because pregnancy provides a natural time-frame for partner testing. Benefits will be assessed by determining what proportion of women (pregnant and nonpregnant) offered testing desire it, what proportion of tested women adequately comprehend the significance of the test results (positive or negative), and what proportion of tested women get their partner tested. Burdens to be assessed are anxiety, lack of comprehension, request for prenatal diagnosis despite low risk, and costs of the program. Providers of reproductive services who agree to participate will be divided into two matched groups; pretest education will be delivered to patients of one group by the primary care provider and to patients of the other group by a trained genetic counselor. Each tested patient will be evaluated for benefits and burdens experienced in order to answer four critical questions. First, is the primary are provider willing to offer free testing in view of the educational burden imposed by a complex message? Second, can the primary care provider be trained to provide pretest education in such a manner that individuals who are unlikely to benefit from the information are not tested? Third, are pregnant patients more likely to benefit from carrier testing than nonpregnant patients? Fourth, can it be shown that, with the proposed combination of improved test sensitivity and proper attention to education, the benefits of population C.F. carrier screening outweigh the burdens?